In recent years, various types of information devices such as television sets, mobile phones, PDAs (Personal Digital Assistants) have gained prevalence and entered into people's lives. Thus, users need to manipulate information devices in many scenes of their usual lives. Usually, in realizing a device manipulation, a user utilizes a hand to input an input command via an input means (interface section) such as a button. However, in situations where both hands are full because of tasks other than a device manipulation, e.g. household chores, rearing of children, or driving, it is difficult to make an input by using an interface section and it is impossible to realize a device manipulation. Therefore, there are increasing needs of users to manipulate information devices in every kind of situation.
In answer to such needs, input means utilizing biological signals from a user has been developed. For example, Non-Patent Document 1 discloses a technique that utilizes an event-related potential of electroencephalogram for distinguishing an option which a user wishes to select. To specifically describe the technique described in Non-Patent Document 1, options are randomly highlighted, and a P3 component of an event-related potential which appears about 300 ms after a point in time that an option was highlighted is utilized to enable distinction of the option which the user wishes to select. According to this technique, a user is able to identify an option which he or she wishes to select, without using a hand.
As used herein, an “event-related potential” refers to a transient potential fluctuation in the brain which occurs in temporal relationship with an external or internal event. An electroencephalogram interface section 100 utilizes an event-related potential which is obtained from a stimulation to the visual sense as an external event. For example, within the event-related potential for a visual stimulation, a so-called P3 component may be utilized to perform processing such as switching of channels, selection of a program genre of which viewing is desired, and sound volume level adjustment. The “P3 component” refers to a positive component of the event-related potential which appears in a time slot of 250 ms to 500 ms after a target stimulation is presented, regardless of the type of sensory stimulation such as auditory sense, visual sense, or somatic sensation.
For an application of the event-related potential to an interface, it is important to distinguish the event-related potential (e.g., the visual P3 component) of a subject with a high accuracy. Therefore, it is necessary to accurately measure a biological signal and accurately distinguish the measured biological signal with an appropriate distinction technique.
In order to accurately measure a biological signal, it is commonplace to calibrate the measurement equipment so that the data which is measured with the measurement equipment is adjusted to accurately present the biological information of a user. For example, Patent Document 1 discloses a technique which, in order to accurately measure the line of sight of a user, calibrates the measurement equipment before measuring the line of sight, and establishes a matched coordinate system between the measurement equipment and the line of sight of the user.
On the other hand, appropriate distinction methods have been devised which account for individual differences appearing in the components of the event-related potential. For example, Patent Document 2 discloses a technique which provides an improved distinction ratio by changing the distinction method for every user. Rather than applying a single criterion to the distinctions for all users, this technique previously generates a template for each individual from an arithmetic mean waveform of an event-related potential regarding a situation to be examined, and distinguishes a component of the event-related potential by using the template. For details concerning individual differences in the event-related potential, see Non-Patent Document 2, for example.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2005-312605    [Patent Document 2] The pamphlet of International Laid-Open No. 05/001677    [Non-Patent Document 1] Emanuel Donchin and two others, “The Mental Prosthesis: Assessing the Speed of a P300-Based Brain-Computer Interface”, TRANSACTIONS ON REHABILITATION ENGINEERING 2000, Vol. 8, June 2000    [Non-Patent Document 2] Hiroshi NITTONO, “Event-Related Potential Guidebook For Psychology”, Kitaoji Shobo, 2005, p. 32